The invention relates to a safety switching arrangement having at least two break switches connected in series to an evaluation unit which initiates a safety signal when at least one of the break switches opens and determines which of the break switches has opened.
It is already known (W. Grxc3xa4f, Maschinensicherheit [Machine safety], Hxc3xctig-Verlag 1997, pages 108-111) for safety switches to be linked in series in order to protect danger points, in the field of safety technology. This is used, for example, in emergency-off circuits in transfer lines and on conveyor belts. In order to determine the respective location of the tripped safety switch in the event of operation, each safety switch is provided with diagnosis contacts which are operated with the opening of the safety switches and are connected by individual lines to the evaluation unit. However, this known safety switching arrangement requires highly complex wiring due to the requirement for a cable link from each diagnosis contact to the evaluation unit. Installation and commissioning are complex. Numerous PLC (programmable logic control) inputs are required on the evaluation unit.
It is an object of the invention to provide a safety switching arrangement of the generic type mentioned above, whose wiring complexity is considerably reduced and which is simple to install and to place in operation.
The idea of the invention is thus that, whenever the break switch opens, a code signal that is characteristic of it is initiated and is supplied to the evaluation unit via a line which is common to all or a plurality of break switches. Consequently, there is no need for the previously required star-configuration wiring for the diagnosis contacts provided on the break switches; this is replaced by serial linking of the diagnosis signals. This avoids additional PLC inputs on the evaluation unit.
The code signal generator associated with each break switch expediently has an associated make switch which is operated jointly with it and activates the associated code signal generator when it closes.
While in one embodiment of the invention the wiring is less complex, another embodiment has the advantage of strict isolation of the diagnosis and safety circuit, leading to simpler evaluation logic in the evaluation unit.
A further option for producing the code sequence and the code signal is for the mechanical force when the safety break switch is operated to be used to produce a short electronic signal. In this case, there is no need for any additional voltage supply or the wiring complexity required for this purpose. All that need be done is for the safety break switch to be appropriately modified.
Thus, when the associated safety break switch is operated, each code signal generator applies a unique code sequence either to the safety path formed by the line sections or to the single diagnosis line provided in addition for this purpose. The safety path (safety line and safety line sections) is closed in the normal, unoperated state.
An ASICS or microprocessor can be programmed with a unique code sequence or a unique code signal, which is emitted when the break switch is operated. One embodiment of the invention uses a special voltage supply which is common to all code signal generators for this purpose. However, this voltage supply may also possibly be obtained from the safety path or the diagnosis line. Furthermore, commercially available safety switches may still be used, which then just need to be equipped with appropriate additional electronics.
The code signal generators preferably have an ASICS or a microprocessor for generating the code signals.
The code signal of the code signal generators may either be applied to the safety or diagnosis line, by the make switches being incorporated in an activation line of the microprocessor and the signal output being continuously connected to the safety or diagnosis line, or by the microprocessor being continuously activated and the make switches being arranged in the signal output.
A test signal for fault identification is expediently output at the test-out connection, and is read back at the test-in connection. If a break switch is operated, the data flow is interrupted. At the same time, the make switch is closed, resulting in the code sequence produced by the associated code signal generator being modulated onto the safety path or the diagnosis line. The test-in or diagnosis-in connection identifies this code sequence and associates this sequence with the corresponding break switch via a connection table which is produced during installation. Each safety switch is given a unique code sequence, which is allocated only once, in the factory.
The invention has the advantage that there is no need for the star-configuration wiring of the diagnosis contacts, and the wiring complexity for the safety path can thus be reduced. Furthermore, no individual diagnosis inputs are required on the evaluation unit. This results in an additional saving in the area of local inputs/outputs. Intelligent controllers and local inputs/outputs already provide for the evaluation of test signals, so that no major additional development complexity is required here.
The invention is not limited to emergency-off switching arrangements but may also be applied to the linking of all safety device outputs having contacts, such as guard gate switches, non-contacting protective devices, position switches, two-hand controllers, etc.
Redundant safety paths are used to comply with relatively stringent safety classes. The circuit need not be expanded for this purpose. Installation and commissioning are simplified by saving wiring and by using existing system configuration aids, such as PC tools.
The invention does not represent a bus system, and thus avoids the following disadvantages which are intrinsic with a bus system:
addressing of the individual bus subscribers;
avoidance of data collision by means of complex message procedures;
use of special ASICS for bus connection.